In the description herein, an aggregate of minute metal wire having a thickness of approximately 200 nm or less is referred to as “nanowires”. When the nanowires are compared to powder, the respective wire correspond to “particle” constituting the powder, and the nanowires correspond to “powder” as an aggregate of particle.
Silver nanowires are expected as a conductive material for imparting conductivity to a transparent substrate. By coating a liquid containing silver nanowires (i.e., a silver nanowires ink) on a transparent substrate, such as glass, PET (polyethylene terephthalate) and PC (polycarbonate), followed by removing the liquid component by evaporation or the like, the silver nanowires are in contact with each other on the substrate to form a conductive network, thereby achieving a transparent conductor. For a transparent conductive material, a metal oxide film represented by ITO has been mainly used for such purposes as a transparent electrode. However, the metal oxide film has defects including the high film forming cost, the low resistance to bending, which may prevent the final product becoming flexible, and the like. A conductive film for a touch-sensitive panel sensor, which is one of the major applications of the transparent conductor, is demanded to have high transparency and high conductivity, and the demand in visibility thereof is also increasing in recent years. An ordinary ITO film necessarily has an increasing thickness for enhancing the conductivity thereof, but the increase of the thickness may decrease the transparency, and the visibility may not be improved.
Silver nanowires are expected to avoid the aforementioned defects peculiar to the metal oxide film represented by ITO.
Known production methods of silver nanowires include a method of dissolving a silver compound in a polyol solvent, such as ethylene glycol and the like, and depositing metallic silver having a linear shape by utilizing the reduction power of the polyol as the solvent in the presence of a halogen compound and PVP (polyvinylpyrrolidone) as a protective agent (PTLs 1 and 2 and NPL 1).